Day to Flower, Day to Complete Flowering and Flowering Period of Thai Soybean Varieties as Affected by Extended Photoperiods.

Abstract

The study on reproductive growth of soybean as affected by different photoperiods, simulated by artificial fluorescence light, was conducted between 1979-80 using soybean varieties S.J.1, S.J.2, S.J.4, Clark 63 and Williams. As 2 hours photoperiod was extended, days to flower of all soybean varieties were 12-14 days delayed. Days to complete flowering were also delayed as daylength extended. By simulated daylength, so that soybean plants would received the photoperiods as if they were grown at 13ºN, 23 ºN and 34 ºN latitude, this was found to affect the days to flower, days to complete flowering, and number of flowers of S.J.1, S.J.2, S.J.4 and Williams varieties of soybean. Daylength given at equivalent of 34 ºN latitude caused the delay in flowering of all soybean varieties. Williams soybean was sensitive to extended daylength than S.J. soybean. Since the days to flower and complete flowering of soybean varieties were delayed when different photoperiods occurred at the early growth stages, which would indicate that the flowering induction process of soybean took place at the early growth, presumably at the unifoliate leaf stage.